I am going to be signing off for the night so I just wanted to cover a few things for you.
It is very rare for an abscess to be so bad that it requires a tail amputation. If he is on medications such as antibiotics or pain meds then this can cause the vomiting you are seeing. Green vomit normally indicated violent vomiting as this tells use that she is pulling liquid from the intestines and not just the stomach.
Abscess themselves can make cats fairly ill.
What you could try is Pepcid AC at a dose of 1/4 of a 10 mg tablet every 12 hours to settle the stomach. Offer bland food such as boiled chicken, chicken baby food ( be sure there are no onions or garlic in the ingredients) or tuna. If she is on meds I would try to do the following.
Give the Pepcid 1st. wait 30 minutes and then give a little food. If she eats wait 20 minutes and then offer medications.
Because she is under a vets care , is a senior kitty and is not eating if she is no better in the morning I would give your vet a call and let them know what is going on.
I hope this helps and she feels better soon. Please reply back if you have additional questions and I will be happy to continue. If you have no additional questions please take a few moments to provide a rating so that justanswer is notified that your concerns have been addressed.